1. Field of the Invention
The present invention relates to a water-cooled engine including at least two exhaust valves in correspondence to each combustion chamber.
2. Description of the Related Art
Disclosed in Japanese Patent Application Laid-open No.3-168353 is an engine in which an exhaust passage extending from a single exhaust valve mounted for each of combustion chambers in a cylinder head opens at its downstream end into a cylinder head/cylinder block coupling surface. Disclosed in Japanese Patent Application Laid-open No.63-253157 is an engine in which a pair of exhaust passages extending from two exhaust valves mounted for each of combustion chambers open at their downstream ends into an outer surface of a cylinder head different from a cylinder block/cylinder head coupling surface.
When the downstream ends of the pair of exhaust passages from the two exhaust valves mounted for each of combustion chambers open into the cylinder block/cylinder head coupling surface, a partition wall partitioning both the exhaust passages is heated to an extremely high temperature by a heat of an exhaust gas and hence, it is necessary to take account of the shape of a cooling water jacket so as to be able to effectively cool the partition wall.